I Just put a new motor and i only had 3 in the car when it came out. But i was Looking under the car when i was changing the oil, i have a place for a fourth O2. Is this really a place for an 02 or is it a plug i just didnt plug in. Its a square plug right beside the starter.
thanks peoples
Steven

 

There are four O2 sensors on a 97 Z28... One on each side of the headers, one before the cat, and one after the cat...

 

have you ever ran your car? I have about the same things you have done

 

yea i have run it... but i can only run 1/8 mile because its conv... all times run low 7's... the one time i did a 1/4 mile pass they would not give me my slip and kicked me off the track...

 

Does a 96Z have 4 O2 sensors as well?

 

Yes

 

Hopefully everyone realizes that this post from 9 years ago is incorrect with regard to the locations. The OBD-II cars have a pre-cat O2 sensor for each bank of the engine, in front of each of the two cats, and an after-cat O2 sensor downstream of each of the two cats.

 

What problems could you have if you dont run all the O2 Sensors?

 

The two after cat sensors are used mainly to monitor the cats. They alledgedly have a small influence on the A/F ratio when they detect a failed cat, but I don't think anyone has ever noticed it. If you delete the after cat sensors, you will get a code for the missing sensors. They can be replaced with O2 "sims" or you can have the after cat sensors tuned out of the PCM.

The pre cat sensors control the engine's A/F ratio. The PCM makes a bunch of calculations to determine how much fuel to inject, based on the mass of the incoming air. The O2 sensors tell the PCM whether it is making the correct calculations. IF there is a change in the engine that affects the A/F ratio, the PCM uses feedback from the O2 sensors to determine "long term fuel corrections" that bring the A/F ratio back where it belongs. It does that to control the A/F ratio used for part throttle operation. But it applies what it learned to WOT operation in most instances.

If you remove the pre cat sensors, you remove the PCM's ability to correct for changes in the engine that affect A/F ratio. It is possiblle to eliminate the O2 sensors by running the PCM in "open loop", where it isn't looking for the feedback from the O2 sensors, but you have to tune very carefully to insure you get the fuel correct, and if there are any changes made to the engine, you'll have to go back an retune more frequently.

 

Great description. Thanks a bunch.

My car has No cats. There is one 02 Sensor on each long-tube and one on the single pipe about mid car. The one about mid-car isn't wired up, but wouldn't be hard to do so. I plan on wiring it back up regardless, but I dont believe its causing my high idle problem while driving. I have read several threads about the IAC needing replaced or cleaned. I have also read several things about vacuum leaks causing this problem. I am going to try to check out these things today. The car only idles high when its rolling. Once you come to a stop, its idling around 800-1000rpm. Thanks again

 

How high does it idle when it's rolling? The PCM raises the idle speed when the vehicle is moving.

 

2-3k

 

Not supposed to be that high. Have you checked for binding throttle cable/linkage?

 

Sounds like somebody had a wideband O2 on it and left the sensor in place instead of installing a plug. You might want to pull it out and see if it has a PN you can check before you wire it up to anything especially if there are no codes being set.

I would say to clean the IAC really well and datalog it to see what is actually going on when the problem occurs.

 

I will double check this.

It doesn't idle down slowly when the car is sitting still. I was thinking if the cable was binding, it would do this then as well.